1. Field of the Invention
The present invention relates to a pitch driving unit for a wind-turbine rotor blade in which the pitch angles of wind turbine blades are changed by hydraulic actuators, and to a wind power generator equipped with the same.
2. Description of Related Art
Standard propeller-type wind power generators are equipped with a wind-turbine rotor blade in which a plurality of wind turbine blades are mounted to a rotor head serving as a rotation center. These wind power generators are configured in such a manner that the wind-turbine rotor blade is rotatably supported by a nacelle that is supported at the upper end of a tower in a manner allowing yawing, and the wind-turbine rotor blade rotates by receiving wind power, so that a generator installed in the nacelle is driven to generate electricity. In the case of an up-wind wind power generator, yaw driving control of the nacelle is performed so that the rotation center axis of the rotor head (wind-turbine rotor blade) is constantly pointed in the windward direction to allow efficient power generation.
In recent years, as disclosed in U.S. Pat. No. 7,658,594 and so on, a pitch driving unit is provided which rotates individual wind turbine blades provided on the wind-turbine rotor blade relative to the rotor head by using a hydraulic driving source or the like to change the pitch angles (attack angles) of the individual wind turbine blades. With this pitch driving unit, when the wind is weak, the wind turbine blades are rotated to a fine side at which the pitch angles are increased, and when the wind is strong, the wind turbine blades are rotated to a feather side at which the pitch angles are decreased. This allows the generator to efficiently generate electricity in the vicinity of a desired rotational speed.
The pitch driving unit of the wind power generator disclosed in U.S. Pat. No. 7,658,594 is equipped with hydraulic cylinders serving as actuators for rotating the individual wind turbine blades, a hydraulic pump that supplies oil to the hydraulic cylinders, a high-pressure oil line that guides the oil discharged from the hydraulic pump to the hydraulic actuators, a low-pressure oil line that returns the oil discharged from the hydraulic actuators to the hydraulic pump, and an oil tank that stores the oil, all of which are installed inside the rotor head.
Accommodating all the components constituting the pitch driving unit inside the rotor head in this manner eliminates the need to pass a hydraulic line between the rotating rotor head and the fixed nacelle via a rotary joint. This can therefore omit the rotary joint, which is expensive and is prone to cause oil leakage, thus resulting in much time for maintenance, and thus considerably reducing the manufacturing cost of the wind power generator and eliminating the portion having the highest risk of oil leakage.
The pitch driving unit of U.S. Pat. No. 7,658,594 is provided with a snorkel-like air bleed pipe in an oil tank to allow the oil tank to be disposed in the rotating rotor head. The air bleed pipe is supported so as to be rotatable about the rotation center axis of the rotor head. A weight is provided at the opposite side of the vent hole of the air bleed pipe, with the rotation center axis of the air bleed pipe interposed therebetween. The mass of this weight allows the vent hole of the air bleed pipe to always project higher than the oil level in the oil tank irrespective of the rotation of the oil tank, thus allowing good ventilation.
However, the pitch driving unit disclosed in U.S. Pat. No. 7,658,594 has the possibility that the oil may spout out from the air bleed pipe, even if it is of a rotating type, to the interior of the rotor head depending on the degree of waviness of the oil surface, thus contaminating the interior of the rotor head because the oil tank has a very complicated structure, and moreover, it opens to the atmosphere through the air bleed pipe.
Furthermore, there is the problem that, even if the oil does not spout directly from the air bleed pipe, oil mist (mist-like oil) in the oil tank comes out of the air bleed pipe during ventilation with the air bleed pipe, thus contaminating the interior of the rotor head with the oil content. Moreover, because the oil is always mixed with air in the rotating oil tank, there are the problems that the oil is degraded by oxidization and that foreign substances tend to get mixed therein.
Furthermore, even if the oil tank is installed not in the rotor head but in the nacelle, there is a high possibility that the hydraulic pump takes in the air in the oil tank when the oil level becomes low because the oil tank opens to the atmosphere, and thus air is present on the surface of the stored oil. This hinders the correct operation of the pitch driving unit; therefore, it is necessary to consider increasing the amount of oil stored in the oil tank and to dispose the intake portion of the oil pump deep in the stored oil, so that the oil pump sucks in as little air as possible.
This increases the size of the oil tank, and thus, many times as much as oil as the pitch driving unit actually needs must be stored. This impairs the interior layout of the rotor head or the nacelle in which the oil tank is disposed, thus making it difficult to design, and increases the amount of oil consumed, which is not desirable in terms of cost and environment.